03-dynamic-facts.js

'use strict'
/*
 * This example demonstrates computing fact values at runtime, and leveraging the 'path' feature
 * to select object properties returned by facts
 *
 * Usage:
 *   node ./examples/03-dynamic-facts.js
 *
 * For detailed output:
 *   DEBUG=json-rules-engine node ./examples/03-dynamic-facts.js
 */

require('colors')
const { Engine } = require('json-rules-engine')

// example client for making asynchronous requests to an api, database, etc
const apiClient = require('./support/account-api-client')

async function start () {
  /**
   * Setup a new engine
   */
  const engine = new Engine()

  /**
   * Rule for identifying microsoft employees taking pto on christmas
   *
   * the account-information fact returns:
   *  { company: 'XYZ', status: 'ABC', ptoDaysTaken: ['YYYY-MM-DD', 'YYYY-MM-DD'] }
   */
  const microsoftRule = {
    conditions: {
      all: [{
        fact: 'account-information',
        operator: 'equal',
        value: 'microsoft',
        path: '$.company' // access the 'company' property of "account-information"
      }, {
        fact: 'account-information',
        operator: 'in',
        value: ['active', 'paid-leave'], // 'status'' can be active or paid-leave
        path: '$.status' // access the 'status' property of "account-information"
      }, {
        fact: 'account-information',
        operator: 'contains',
        value: '2016-12-25',
        path: '$.ptoDaysTaken' // access the 'ptoDaysTaken' property of "account-information"
      }]
    },
    event: {
      type: 'microsoft-christmas-pto',
      params: {
        message: 'current microsoft employee taking christmas day off'
      }
    }
  }
  engine.addRule(microsoftRule)

  /**
   * 'account-information' fact executes an api call and retrieves account data, feeding the results
   * into the engine.  The major advantage of this technique is that although there are THREE conditions
   * requiring this data, only ONE api call is made.  This results in much more efficient runtime performance.
   */
  engine.addFact('account-information', function (params, almanac) {
    return almanac.factValue('accountId')
      .then(accountId => {
        return apiClient.getAccountInformation(accountId)
      })
  })

  // define fact(s) known at runtime
  const facts = { accountId: 'lincoln' }
  const { events } = await engine.run(facts)

  console.log(facts.accountId + ' is a ' + events.map(event => event.params.message))
}
start()

/*
 * OUTPUT:
 *
 * loading account information for "lincoln"
 * lincoln is a current microsoft employee taking christmas day off
 *
 * NOTES:
 *
 * - Notice that although all 3 conditions required data from the "account-information" fact,
 *   the account-information api call is executed only ONCE.  This is because fact results are
 *   cached by default, increasing performance and lowering network requests.
 *
 * - See the 'fact' docs on how to disable fact caching
 */